/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression.spel.ast;

import java.math.BigDecimal;
import java.math.BigInteger;

import org.springframework.expression.EvaluationException;
import org.springframework.expression.Operation;
import org.springframework.expression.TypedValue;
import org.springframework.expression.spel.ExpressionState;
import org.springframework.expression.spel.SpelEvaluationException;
import org.springframework.expression.spel.SpelMessage;
import org.springframework.util.Assert;

/**
 * Decrement operator.  Can be used in a prefix or postfix form. This will throw
 * appropriate exceptions if the operand in question does not support decrement.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @author Giovanni Dall'Oglio Risso
 * @since 3.2
 */
public class OpDec extends Operator {

    private final boolean postfix;  // false means prefix


    public OpDec(int pos, boolean postfix, SpelNodeImpl... operands) {
        super("--", pos, operands);
        this.postfix = postfix;
        Assert.notEmpty(operands, "Operands must not be empty");
    }


    @Override
    public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
        SpelNodeImpl operand = getLeftOperand();

        // The operand is going to be read and then assigned to, we don't want to evaluate it twice.
        ValueRef lvalue = operand.getValueRef(state);

        TypedValue operandTypedValue = lvalue.getValue();  //operand.getValueInternal(state);
        Object operandValue = operandTypedValue.getValue();
        TypedValue returnValue = operandTypedValue;
        TypedValue newValue = null;

        if (operandValue instanceof Number) {
            Number op1 = (Number) operandValue;
            if (op1 instanceof BigDecimal) {
                newValue = new TypedValue(((BigDecimal) op1).subtract(BigDecimal.ONE), operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof Double) {
                newValue = new TypedValue(op1.doubleValue() - 1.0d, operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof Float) {
                newValue = new TypedValue(op1.floatValue() - 1.0f, operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof BigInteger) {
                newValue = new TypedValue(((BigInteger) op1).subtract(BigInteger.ONE), operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof Long) {
                newValue = new TypedValue(op1.longValue() - 1L, operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof Integer) {
                newValue = new TypedValue(op1.intValue() - 1, operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof Short) {
                newValue = new TypedValue(op1.shortValue() - (short) 1, operandTypedValue.getTypeDescriptor());
            } else if (op1 instanceof Byte) {
                newValue = new TypedValue(op1.byteValue() - (byte) 1, operandTypedValue.getTypeDescriptor());
            } else {
                // Unknown Number subtype -> best guess is double decrement
                newValue = new TypedValue(op1.doubleValue() - 1.0d, operandTypedValue.getTypeDescriptor());
            }
        }

        if (newValue == null) {
            try {
                newValue = state.operate(Operation.SUBTRACT, returnValue.getValue(), 1);
            } catch (SpelEvaluationException ex) {
                if (ex.getMessageCode() == SpelMessage.OPERATOR_NOT_SUPPORTED_BETWEEN_TYPES) {
                    // This means the operand is not decrementable
                    throw new SpelEvaluationException(operand.getStartPosition(),
                            SpelMessage.OPERAND_NOT_DECREMENTABLE, operand.toStringAST());
                } else {
                    throw ex;
                }
            }
        }

        // set the new value
        try {
            lvalue.setValue(newValue.getValue());
        } catch (SpelEvaluationException see) {
            // if unable to set the value the operand is not writable (e.g. 1-- )
            if (see.getMessageCode() == SpelMessage.SETVALUE_NOT_SUPPORTED) {
                throw new SpelEvaluationException(operand.getStartPosition(),
                        SpelMessage.OPERAND_NOT_DECREMENTABLE);
            } else {
                throw see;
            }
        }

        if (!this.postfix) {
            // the return value is the new value, not the original value
            returnValue = newValue;
        }

        return returnValue;
    }

    @Override
    public String toStringAST() {
        return getLeftOperand().toStringAST() + "--";
    }

    @Override
    public SpelNodeImpl getRightOperand() {
        throw new IllegalStateException("No right operand");
    }

}
